Colour sorting machines



Dec. 4, 1962 H. FRAENKEL 3,066,797

COLOUR SORTING MACHINES Filed Nov. 13, 1958 5 Sheets-Sheet l V Z/ i A Ol T J 3/ 25 Inventor:

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&1?? g a B Attorr fs Dec. 4, 1962 H. FRAENKEL 3,066,797

COLOUR SORTING MACHINES Filed Nov. 13, 1958 5 Sheets-Sheet 2 lu s Attorneys Dec. 4, 1962 FRAENKEL 3,066,797

COLOUR SORTING MACHINES 5 Sheets-Sheet 5 Filed Nov. 13, 1958 By. D o

Q 64 40 4 27 2 AtAo neys Dec. 4, 1962 H. FRAENKEL comma SORTING MACHINES 5 Sheets-Sheet 4 Filed Nov. 13, 1958 Dec. 4, 1962 H. FRAENKEL COLOUR SORTING MACHINES 5 Sheets-Sheet 5 Filed Nov. 13, 1958 INVENTOR Herbert Froenkal I l I l I I l I I I I I I 1 l I I [.llfilllllll mm m 2E mm BY M @ ATTORNEYS United States Patent Ofifice 3,066,797 Patented Dec. 4, 1962 spears! coroun sonrrrso MAcnmns Herbert Fraenkel, London, Engiand, assignor to R. W.

This invention concerns improvements in the sorting of objects by colour, and although it is not so restricted, the invention is of particular use where it is desired to sort by grades of colour rather than by shades of colour, that is to say where it is desired to sort in accordance with the relative reflectivity in two or more parts of the spectrum rather than in accordance with whether there is more or less light reflected by the objects within one part only of the spectrum.

in effecting colour sorting it is desirable to use backgrounds against which light reflected from the object under examination may be compared. Such backgrounds are selected to reflect the same average intensity of visible light (so far as the photocell examining the object is concerned) as the object itself. Backgrounds are employed as a convenient way of reducing the influence of the size of the object upon the amount of light received by the photocell. In fact, in the case where the background perfectly matches a desired object, the variation of light received by the photocell is entirely due to variation in reflectivity on the part of the object under examination and this is of course what is to be aimed at. It will, therefore, be appreciated that it is necessary to vary the backgrounds with variation of the objects being sorted and that it is also necessary to select a background suitable for the particular type of sorting which is to be effected.

Accordingly, if the sorting is to be by grades of colour, that is to say, if the sorting is to be in accordance with the relative reflectivity in two or more parts of the spectrum, then it is necessary to employ backgrounds which contain the different colours being used. Assuming, for example, that sorting is to take place by reference to two different colours, the backgrounds will need to have a reflectivity which is chosen to be correct for two photocells each one of which has a different colour response. Whereas, therefore, in the case of single colour sorting it may be necessary to choose one of, say, twenty graduated backgrounds, in the case of double colour sorting, it would normally be necessary to choose one of several hundred graduated backgrounds which vary in colour and brightness. Moreover, whereas in the case of single colour sorting it is merely necessary to choose a background which is lighter or darker, in the case of double colour sorting it is necessary to choose from backgrounds varying also in the two colours, which would ordinarily be a very onerous task.

According, therefore, to one particular aspect of the present invention, a sorting machine for sorting articles by colour comprises a background support member, a light source adapted to irradiate a background carried by the support member and to irradiate objects to be sorted, photo-electric viewing means positioned to receive light from each said object and from the background, means, controlled by the photo-electric viewing means, for separating desired from undesired objects, and means for varying the intensity of the reflection from a background carried by the support member.

The ability readily to vary the intensity of the reflection of the background considerably reduces the difficulty in selecting the correct background for use in multiple colour sorting.

The variation of the intensity of the reflection of the background may be effected by varying the amount of 2 light falling on the background, e.g. by varying the dis tance between the background and the light source.

The variation of the amount of light falling on the background can also be eflected by interposing an optical wedge (i.e. a member different portions of which absorb different amounts of light or different wavelengths of light) between the background and the light source. Alternatively an adjustable shutter or mask may be disposed in front of the light source so as to be movable to alter the amount of light falling on the background.

Alternatively, there may be interposed between the background support member and the light source a cylinder which is coloured in different areas with varying relative amounts of the two or more colours in which sorting is to take place.

Again, instead of interposing such a cylinder between the background support member and the light source, the cylinder may itself provide the background, so that, by rotating the cylinder what are, in effect, a large number of diflerent backgrounds can be obtained.

it is preferred to view the object to be sorted from a number of different directions. This requires of course the provision of a corresponding number of background support members and where such a plurality of background support members is provided it is preferred to interconnect the background support members together and to provide means for simultaneously adjusting the position of each background support member with respect to the light source.

Where objects such, for example, as beans and more particularly roast coffee beans are fed to a colour sorting machine difficulties may arise because most of the light reflected by such objects is the result of specular reflection. In the case of such objects an accurate meas: urement of the colour of the object is very difficult as a slight angular twist of the surface of the object can very substantially affect the amounts of light captured by the lenses, of the apparatus employed, which project an image of the object onto a scanning slot in front of the photocell.

According therefore, to another aspect of the invention, a sorting machine comprises means for illuminating an object to be sorted with plane polarised light, photoelectric viewing means positioned to receive light from the object so illuminated, means, controlled by the photoelectric viewing means, for separating desired from undesired objects, and an analyser disposed in the path of the light from the object to the photo-electric means, the plane of polarisation of the analyser being crossed with respect to the plane of polarisation of the polarised light produced by the first mentioned means.

The sorting of articles in accordance with their colour is commonly effected during the free fall of the articles, each article, in the course of its fall, passing a photoelectric viewing system. Where double colour sorting is being effected, it is clearly desirable that the amount of light transmitted to the two photo-electric means, one for each colour, is not affected by the position of the object along the line of fall or by limited longitudinal departure of the object from a desired line of fall.

According therefore to yet another aspect of the invention, there is provided a sorting machine comprising a light conducting member having a plurality of limbs which meet substantially at a common point, lens means for focusing an image of an object to be sorted onto or adjacent to the said common point, photo-electric viewing means disposed at the outer end of each of the limbs of the light conducting member, and means, controlled by the photo-electric viewing means, for separating desired from undesired objects.

In a preferred form of this aspect of the invention, a sorting machine is provided with an objective which spea /9v focuses an image of an object to be sorted onto a viewing slot, and a lens system, on the opposite side of the slot, for focusing the objective onto a point adjacent to the point of separation of the limbs of a forked transparent light conducting rod (eg of methyl methacrylate) each of whose branches leads to a photocell.

Sorting machines for sorting articles in accordance with their colour are, of course, provided with means for ejecting undesired articles. Amongst the means which have previously been suggested for this purpose are, on the one hand, means for directing an air jet onto the undesired article so as to remove it from the rest of the articles, and, on the other hand, a mechanical ejector in the form of a magnetically operated lever. Either of these means involve the use of a very rapidly moving body acting as a valve or plunger and this body has to be rapidly returned to its inoperative position after each excursion.

According therefore to yet another aspect of the invention, a sorting machine comprises ejector means for removing undesired articles from a group or stream of articles, and liquid damping means for damping the operation of the moving parts of the ejector means, when the said moving parts return to their inoperative position.

The signals received from the photocell or photocells of a colour sorting machine, which signals control operation of the said ejector means, are commonly amplified by an alternating current coupled amplifier, such an amplifier being used because of the diifieulty of stabilisation of a directly coupled amplifier over long periods of time. Use of an alternating current coupled amplifier, however, may cause difiiculty because of changes in the direct current level of the signal being fed to the grid of a valve discriminating between positive and negative signals or comparing the relative magnitude of these signals. As a result, and because the average colour and rate of flow of the objects being viewed may vary, the datum with respect to which the said valve effects its comparisons is liable to change during the course of a sorting operation.

According therefore to yet another aspect of the invention, there is provided a sorting machine comprising photoelectric viewing means adapted to receive light from objects to be sorted, said means being connected to and being adapted to pass signals to an electronic comparator adapted to distinguish desired from undesired objects, photo-electric detecting means disposed adjacent the viewing means and adapted to detect the presence or absence of an object before the viewing means, means controlled by the detecting means for, in effect, short-circuiting the comparator when an object is absent from the viewing means, and means con-trolled by the comparator for separating desired from undesired objects.

Thus even though the objects to be sorted are not fed at regular intervals or predetermined times past the viewing means it is ensured that the short-circuiting is always correctly timed. The short-circuiting prevents the sorting being affected by changes in the direct current level of the signal.

Preferably the reflectivity of the background viewed by the said detecting means varies from that of the objects in a region of the spectrum outside that being used for colour sorting (e.g. in an invisible region of the spectrum) and the photo-electric detecting means is made sensitive to this region. Thus, for instance, the background may be illuminated with light, e.g. infra-red light, outside the visible spectrum, while the light falling on the object passes through a filter absorbing infra-red light, the detecting photocell employed being sensitive to this infrared light, and the infra-red light being directed onto this photocell via a lens system employed in the photo-electric viewing means. Preferably, however, the light falling on the background is caused to pass through a glass plate absorbing infra-red light, while the object has directed onto it light containing infra-red and also possibly light which has passed through a filter which transmits infrared light only.

The invention is illustrated, merely by way of example, in the accompanying drawings, in which:

FIGURE 1 is a schematic diagram illustrating the general operation of a machine according to the invention,

FIGURE 2 is a plan view of a frame constituting a part of the machine of FIGURE 1,

FIGURES 3 and 4 illustrate diagrammatically modifications of the frame shown in FIGURE 2,

FIGURE 5 illustrates diagrammatically means provided for overcoming the effects of specular reflection from the objects being sorted,

FIGURE 6 is a section through a practical form of another part of the machine of FIGURE 1,

FIGURES 7 and 8 illustrate diagrammatically further parts of the machine of FIGURE 1, and

FIGURE 9 is a diagrammatic view showing a representative arrangement of the components.

Referring first to FIGURE 1 which shows a diagrammatric representation'of a machine of the present invention, a colour sorting machine comprises an endless belt 1 having a V-shaped recess for the reception of objects 2 (such, for example, as peas or beans) which are to be sorted. It will of course be appreciated that feeding devices other than the endless belt shown in FIGURE 1 may be used if desired.

Objects 2, delivered by the belt 1, are allowed to fall freely therefrom and through a cube-shaped frame 3 having internally reflecting walls. As the objects fall through the frame 3 light from lamps within the frame 3 falls on the objects and the light reflected therefrom is viewed by one or more pairs of photocells or photo-multipliers 4, 5.

Although only one such pair of photocells or photomultipliers 4, 5 is shown, it is preferred to use four such pairs, one at each side of the frame 3.

The photocells or photomultipliers are respectively provided with differently coloured filters 6, 7 so that one of the photocells or photomultipliers of each pair is sensitive to light of one particular colour reflected by the objects 2 while the other photocell or photomultiplier of the pair is sensitive to light of a different colour reflected by the objects 2.

The light received by the photocells or photomultipliers 4, 5 from the objects 2 is transmitted by way of a lens tube 8, which contains an objective 9 for focusing an image of an object 2 onto a scanning slot 10, a lens system generally indicated at 11, and a transparent, light conducting member 12 having a V-shaped portion, the lens system 11. serving to focus an image of the objective 9 onto the point of separation 13 of the limbs of the V.

The outputs of the photocells or photomultipliers 4, 5 are connected across a difference amplifier 14 the output of which in turn controls an electronic comparator 15 which is adapted to distinguish desired from unde sired objects.

When a faulty object 2 falling through the frame 3 is detected by the comparatorlS, a signal is transmitted therefrom to an electrically-controlled ejector device 16. Compressed air is delivered to the device 16 via a line 17, and, as a result of the said ignal, a valve is opened so that the air is allowed to escape as a jet from a nozzle 18 forming part of the device 16. As a result, the faulty object 2 is ejected.

The machine shown schematically in FIGURE 1 will now be described in greater detail with reference to the other figures.

Disposed within the frame 3, whose internal walls 19 (see FIGURE 2) are rendered light reflecting (e.g. by a coating of vitreous enamel) are four light sources or lamps 20 which are disposed adjacent the corners of the frame 3 and are adapted to irradiate an object 2 at the centre of the frame 3. The visible light from the light sources 20, however, which falls on the object 2 is indirect, an infra-red transmitting filter 21 being disposed (for a purpose described below) in the direct path of the light from each light source to the object.

Light from the light sources also falls on background elements 22 each of which is mounted within a background support member 23 constituted by a channel shaped frame into which the background may he slid. As explained above, the backgrounds are selected to reflect the same average intensity of visible light (so far as the photocell examining the object is concerned) as the object itself, the backgrounds being employed as a convenient way of eliminating the influence of the size of the object 2 upon the amount of light received by the respective photocell.

Wedges 24 prevent direct light from the light sources 20 falling on the adjacent background elements 22.

Rotatably mounted in the frame 3 with their centres arranged at the corners of a square are four discs 25, 26, 27, 28. Each disc is connected to each of its adjacent discs by a bar 29 to which the respective background support member 23 is secured. Each adjacent pair of discs are also interconnected by a bar 34 It will be noted that the bars 30 are arranged parallel to the bars 29 but are pivoted to their discs at points which are angularly spaced from the pivot points of the bars 29 by equal amounts of about 90.

The disc 25 has a control arm 31 secured thereto and extending outwardly thereof. The control arm 31 may be moved from the full line to the dotted line position and in so doing will move all four discs through a corresponding angle. This will cause movement of the bars 29 and therefore of the background elements 22 carried thereby. The provision of the two sets of interconnecting bars 29, 3t ensures that movement of the discs 25, 26, 27 and 28 is not prevented by reason of one set of bars being in a dead centre position.

The control arm 31 may be fixed in a desired position by means of a threaded stud 32 having an enlarged head for manual rotation.

As indicated by dotted lines, the movement of the background elements 22, as a result of movement of the control arm 31, is not linear. The background elements, however, are selected to be large relatively to the object 2 so that this non-linearity does not matter.

Thus by moving the control arm 31, all the background elements may be simultaneously moved inwards or outwards. Since the intensity of illumination of the backgrounds varies with the square of their distance from the source of illumination, it is readily'possible in the arrangement shown in FIGURE 2, by moving the control arm 31 to vary the illumination of the background elements by about This ability readily to vary the intensity of the reflection of the backgrounds makes it substantially easier to select the correct backgrounds, i.e. to match the backgrounds with the objects being sorted.

The arrangement shown in FTGURE 2 may be modified, as shown in FIGURE 3, by replacing the background elements 22 and their support members 23 by cylinders 32. Each cylinder 32 has a plastic or metal core around which is wrapped a photographically produced or printed sheet of paper or other material enclosed within a cylinder of a transparent material such as glass or methyl methacrylate. The said sheet may be coloured in different areas with varying relative amounts of the colours in which sorting is to take place. Alternatively the said sheet may constitute an optical wedge (i.e. a member different portions of which absorb different amounts of light or diiferent wavelengths of light) by being formed from celluloid different parts of which are arranged to absorb light to different extents.

The cylinders 32 are mounted on shafts 33 which are geared together by bevel gears 34, a handwheel 35 being provided for rotation of the cylinders.

Thus the parts of the cylinders 32 being viewed will constitute backgrounds and the intensity of the reflection from the cylinders will be altered not by varying their distances from the light sources but by rotating them so as, in efiect, to select dirferent backgrounds.

A further alternative way of varying the intensity of the reflection from the backgrounds is shown schematically in FIGURE 4. In the FIGURE 4 construction, the background elements 22 and light sources 20 are stationary so that the amount of light falling upon the backgrounds cannot be varied by altering the spacing of the light sources and backgrounds. A collimating lens 20, however, is provided in front of each light source 20. Rotatably mounted above the light sources 20 and lenses 20 is a substantially cruciform member 36 having, at the end of each of its arms a downwardly extending portion 37 which, in certain angular positions of the cruciform member 36 will serve as a mask near the lenses 20' so as to reduce the amount of light falling on the backgrounds 22. The cruciform member 36' may be rotated by manually engaging one of its arms. Alternatively means (not shown) may be provided for rotating the member 36.

As explained above, the sorting of some objects, such for example, as roast coffee beans is rendered diflicult by the fact that most of the light reflected by such objects is the result of specular reflection. This problem can, however, be dealt with as indicated schematically in FIGURE 5.

Referring to FIGURE 5 it will be seen that the light falling on an object 2 from each of the four light sources 2%} is collimated by a collimator 38 and passes through a sheet 39 of Polaroid (registered trademark), whereby the object 2 and background elements are irradiated with plane polarised light.

Light received from the object 2 and background elements is reflected by way of the lens tube 8 on to one or both of the photoelectric cells 4, 5 (the latter not being shown in FIGURE 5); one photoelectric cell being used for each colour in which sorting is to be effected. Between the lens tube 3 and the object 2 there is disposed a sheet 40 of Polaroid, the sheet 44} being arranged so as to be crossed with respect to the plane of polarisation of the polarised light reflected by the object 2. That is to say, each of the sheets 39 is crossed with respect to the sheet 4%. The angular dispositions of the sheets 39 and 40 are such that, if the object 2 were a perfect mirror, virtually no light would enter the photocells 4, 5. The difluse reflection of the object 2, however, will cause modification of the polarisation of the light so as to allow some of it to pass through the sheet 44} to the photocells 4, 5.

The reflection from the background elements is, of course, constant once they have been chosen, so they have no eflfect on the modifications of the polarised light caused by the object.

The provision of the four lamps 2i? and their sheets of Polaroid 39 helps to avoid shadows being formed on the object as a result of irregularities on the surface of the object. This permits the object to be viewed, if desired from two more or less diametrically opposed sides, each side having its own suitably crossed. sources of illumination.

As will be seen from FIGURE 1, the objects 2 fall freely through the frame 3 during their inspection by the photocells or photomultipliers 4, 5 which are respectively provided for the two colours in which sorting is to take place. The construction of members 413 indicated schematically in FEGURE l and shown in detail in a practical construction in FIGURE 6 is provided so that the amount of light transmitted to each of these photo cells or photomultipliers is not affected by the position of the object 2, at the moment at which it is viewed, along its line of fall or by limited longitudinal departure of the object 2 from a desired line of fall.

Referring to FIGURE 6, light from the object 2 passes into the lens tube 8 which is provided with a glass dust cover 41, objective 9 comprising lenses 42, 43, scanning slot 10 and a lens system 11 comprising lenses 44, 45. The arrangement is such that the objective 9 focuses the image of the object 2 to be sorted on to the scanning slot 10.

Extending from adjacent the lens system 11 is a rod 12 of a transparent light conducting material, e.g. of methyl methacrylate, the rod 12' forming part of the light conducting member 12 shown in FIGURE 1. The rod 12 is cemented to a plate 46 of transparent light conducting material and a further rod 12" of such material is cemented to the plate 46. The plate 46 is secured to the ground surface 47 of a mirror 43.

The rod 12" is bifurcated into two arms 49, 59 which are arranged substantially along thelimbs of a V. These arms 49, Stl lead respectively to the photocells or photomultipliers 4, 5, the arm 49 being of smaller diameter or section than the arm 50.

Each of the arms 49, 50 has a ground outer end 51 and a colour filter '52 is disposed between the ends 51 and the photocells or photomultipliers 4, 5. Light from the end of the arm 49 is directed onto a mirror 53 by which it is reflected onto the photocell or photomultiplier 4.

The point of separation 13 of the arms 49, 56 (i.e. the apex of the V) is so disposed that the lens system 11 focuses an image of the object 2 onto the point of separation 13 or a point adjacent thereto. It will, therefore, be appreciated that the amount of light transmitted to the photocells or photomultipliers 4, is not affected by the precise position at which the object 2 is viewed. Thus the position of the object along the line of fall or a limited longitudinal departure of the object from a desired line of fall will not substantially affect the relative amounts of light received by the photocells or photomultipliers 4, 5.

Reference will now be made to FIGURE 7 which illustrates the photoelectric detecting means (not shown in FIGURE 1) which uses infrared light to detect the presence or absence of an object before the viewing means. FIGURE 7 also illustrates the construction of the electronic comparator 15 which is shown diagrammatically in FIGURE 1.

The light falling on and reflected by the object 2 comprises both visible light and infrared light, whereas it is arranged that one or more of the background elements 22 reflects less infrared light than the objects 2, or preferably, that the background elements 22 reflect no inf-rared light.

Light from an object 2 and each background element 22 is transmitted through an optical system (not shown) and via the relatively wide viewing aperture in a metal member 55 and the relatively narrow viewing aperture in a filter 56. The latter is adapted to transmit only infrared light except at the said relatively narrow aperture where it is adapted to transmit visible light. The light from the filter 56 falls onto the partially silvered mirror 53'. The latter divides the light into one portion which irradiates the photocell or photomultiplier 4', which is sensitive only to visible light, and another which irradiates, via an infrared transmitting filter 57, a photocell 58 which is adapted to produce a signal only when an object 2, which reflects more infrared light than the background elements 22, is being viewed.

It should be noted that the photocell 4' indicated and described in relation to [FIGURE 7 is intended to repre cut the photocells 4 and 5 (and associated apparatus illustrated in FIGURE 6) used to effect the colour sorting. Of course, only one of these photocells need be used (as indicated by 4) if sorting is to be efiected in only one colour.

The photocell 4- is connected, by way of an amplifier 59 and condenser 60, in the grid circuit of a triode 61 signals from which control operation of the ejector device 16. The photocell 53 is connected by way of an amplifier 62 to a phase splitter 63 adapted to produce two signals in anti-phase. Connected across the phase splitter 63 is a pair of low resistances 64, 65 the latter be- 3 ing connected in a circuit 66 connected to the grid circuit, the circuit 66 including a pair of silicon or valve diodes 67, 68. The triode 61 is biased to cut off by a power source 69.

Accordingly when there is no signal from the phase splitter 63 (i.e. when no object 2 is being viewed) the grid-cathode circuit of the triode 61 is (in efiect, shortcircuited by way of the low resistances 64, 65 and diodes 67, 68. The fact that short-circuiting occurs whenever an object 2 is absent from the view ensures that the datum with respect to which the triode 61 discriminates between desired and undesired objects does not change in the course of a sorting operation. Moreover, even though the rate of fall of the objects 2 past the viewing position is irregular, the short-circuiting will nevertheless be correctly timed.

When an object is viewed by the detecting means, the grid-cathode circuit is again made; a signal received by the photocell (or photocells) 4 is transmitted by the amplifier (or difference amplifier) 59 if the object is to be rejected, the signal raises the potential of the triode grid, so causing the triode to fire, thus sending a signal to the ejector device 16 (FIGURE 1).

Since, in operation, the object 2 is falling in space, infrared light from the object 2 will pass through the unapertured portion of the filter 56 before and after visible light from the object 2 passes through the aperture in the filter 56.

Accordingly the infrared sensitive photocell 58 receives its signal slightly before and continues to receive it slightly after the signal received by the visible light sensitive photocell 4. This arrangement compensates for the effects of delay in the circuit.

The ejector device 16 of FIGURE 1 is shown in detail in FIGURE 8. Referring to FIGURE 8, compressed air from the line 17 is adapted to be directed from the nozzle 18 onto an undesired article 2 so as to remove it. The air nozzle 18 is provided with a valve obturating member 76 for permitting and preventing flow of the jet of air. The valve obturating member '70 is provided at one end of a valve rod 71 which is urged by springs 72, 73 towards the closed or inoperative position in which no air will escape from the nozzle. The end of the rod 71 remote from the nozzle 18 carries the coil 74 of an electromagnetic device 75, the coil being energised in response to a signal from the triode 61 indicating the presence of an undesired object 2. When such a signal is received, the valve rod 71 is retracted against the action of the springs '72, '73 so as to release the jet of air and thus eject the undesired object.

On the de-energisation of the electro-magnetic device, the valve obturating member '70 is pulled by the springs 72, 73 sharply onto its seating so that it would normally rebound therefrom. In order to prevent substantial rebound, however, the valve rod 71 is provided with a flange or projection 76 which, when the valve obturating rod is fully seated, hits an abutment device 77. The abutment device '77, which is carried by springs 73, 79 so as to be resiliently movable in the direction of movement of the valve rod, consists of a cylinder or other container 77 filled with glass wool 77 or similar material and partially filled with a liquid, not shown, which is preferably of high density and low viscosity.

Accordingly when the abutment device 77 is hit by the flange or projection 76, movement of the valve rod 71 is damped, movement of the abutment device 77 being damped by reason of the transfer of energy occurring as a result of the forcing of the liquid in the container past the partial obstructions provided by the glass wool.

Having in mind the foregoing description, a summary of the arrangement of components and further explanation of the operation will be set forth with reference to FIGURE 9 considered in connection with FIGURES l-8. The components in FIGURE 9 are designated by the same 9 reference characters as the structurally illustrated components in FIGURES 1-8.

The following points should be noted:

(1) Polarised light is used to reduce the effects of specular reflection.

(2) Infra-red light is used simply to operate the detecting means, which detects the presence or absence of an. article before the viewing apparatus, it does not produce the signal for ejecting the article.

(3) The signal for ejecting the article comes from a dilference amplifier taking its signal from two photocells, in the simple case illustrated.

Turning to FIGURE 9, light from a lamp 2% passes through an optical system including a polariser 39, and illuminates a background element 22 and an object 2. In the preferred form shown, a glass plate which absorbs infra-red is placed in front of the background element such that no infra-red light reaches the element. Hence no infra-red light can be reflected by the background element.

Further light from the lamp 2% also passes through an infrared transmitting filter 21, and falls onto the object 2. Hence the object 2 is illuminated by both visible light and by infra-red light.

Reflected light from both the background element and the object passes through an analyser 4t), and then to the mirror 53 and associated apparatus described in detail above.

Light passes straight through mirror 53, enters the light splitting device (described in detail with reference to FIG- URE 6) and .thus passes to two photocells 4 and 5. Filters 6 and 7 are placed in front of each photocell, and these are chosen with respect to the colours in which sorting is to be effected. Thus, if peas are being sorted, and it is desired to reject all peas not having a specified minimum biue:yellow ratio, the filters 6 and 7 would be chosen in blue and yellow. The associated electrical circuit and difference amplifier can be adjusted such that if any pea viewed by the apparatus has a low bluezyellow ratio, below the set minimum, the signals from each of the photocells for blue and for yellow, when passed through the difference amplifier will give a resulting signal sufiicient to trigger the comparator 15, as described with reference to FIGURE 7. if the bluezyellow ratio, as measured by the blue and yellow photocells and the difference amplifier, is of an acceptable value, then the signal will not be sun cient to trigger the comparator 15, and thus the ejector device 16 will not be operated.

It is important to zero the electronic comparator when it is not in use, since stray currents could affect the action of the comparator. The circuit conditions are therefore always returned to the same values after each operation. This is done by the photoelectric detecting means which operates on the infra-red signal.

When no object 2 is in view, there will be no infra-red light entering the apparatus or being reflected from mirror 53, since, as explained above, only the objects can reflect infra-red light. With no signal from the photocell 58, the electronic circuit of the comparator is at zero condition, a reference condition to which it always returns.

When an object is in view, infra-red light is reflected into the apparatus, triggers the photocell 58, which acts upon the electronic circuit to render the comparator operable. It should be noted that this does not operate the comparator, but merely renders it operable.

The signal received from the difference amplifier as a result of the light transmitted to the photocells 4-, from the object, then operates or fails to operate the comparator.

As soon as the object has passed from view, the comparator is returned to the reference condition once more by the photoelectric detecting means.

Thus the detecting means acts as a switch, placing the comparator into and out of the circuit, and always bringing it back to its reference condition.

The reason for using two photocells for eflecting sorting is as follows:

It is desired to sort peas, removing, for example, those which are not mature and yellow in appearance (or those which are over-mature, and blue/black in appearance) from those which are mature and of the correct shade of green (is. correct ratio of yellowzblue).

It would be possible to sort these peas by employing a photocell which is sensitive to yellow, and thus measures the amount of yellow contained in any one pea. Peas with more yellow than the specified minimum would be rejected, and all peas with at least the minimum quantity of yellow would be accepted.

However, those peas with at least the minimum quan' tity of yellow may have more than the acceptable amount of blue in them, and thus be dark in appearance, and unacceptable. A further photocell is therefore required, which will be sensitive to blue. This photocell can be adjusted to register when more than the maximum amount of blue is contained in any pea.

Thus two photocells are employed, to sense the yellow and blue components of each green pea, and the signals from these photocells are taken to a diflerence amplifier. The arrangement is such that the ratio yellowzblue for each pea is measured, and if the ratio departs very greatly from the ratio for a perfect green pea, then a signal is produced by the difference amplifier, and this is used to trigger the ejector device.

I claim:

1. A sorting machine for sorting articles by colour comprising means for illuminating a light reflective object to be sorted with plane polarised light to cause light to be reflected by said object, photoelectric viewing means positioned to receive and view light reflected from the object so illuminated, means, controlled by the photoelectric viewing means, for separating from each other objects which respectively have and fail to have a predetermined colour, and an analyser disposed in the path of the light reflected from the object to the photoelectric means, the plane of polarisation of the analyser being crossed with respect to the plane of polarisation of the polarised light produced by the illuminating means.

2. A sorting machine as claimed in claim 1 in which a plurality of illuminated background elements are supported by a plurality of background element support members and a plurality of photoelectric viewing means are provided so that the objects are viewed from a corresponding number of different directions, the background element support members being interconnected so that they may all be simultaneously adjusted in position, whereby the intensity of reflection from the background elements may be brought to any desired value.

3. A sorting machine according to claim 1 including a plurality of photoelectric viewing means, and means for transmitting light from an object being viewed to said photoelectric viewing means, said transmitting means comprising a forked light conducting transparent rod having a plurality of limbs which met substantially at a common point, a photoelectric viewing means being disposed at the outer end of each of the said limbs, and lens means for focusing an image of an object to be sorted adjacent to the said common point.

4. A sorting machine as claimed in claim 3 in which the light conducting member has only two limbs and in which one of the photoelectric viewing means is sensitive to light of one colour and the other photoelectric viewing means is sensitive to light of another colour.

5. A sorting machine as claimed in claim 1 comprising a shaft and a cylinder mounted thereon and illuminated by said illuminating means, different parts of said cylinder being coloured in ditferent areas with varying relative amounts of the colours in which sorting is to take place.

6. In a sorting machine for sorting articles by colour an ejector means having moving parts for removing articles which fail to have a predetermined colour from a group of articles, and damping means having a valve obturating member for damping the operation of the moving parts of the ejector means, when the said moving parts return to their inoperative positions.

7. A sorting machine for sorting objects by colour comprising photoelectric viewing means adapted to receive light fro-m objects to be sorted, an electronic comparator adapted to distinguish from each other objects which respectively have and fail to have a predetermined colour, the photoelectric viewing means being connected to and being adapted to pass signals to the comparator, photoelectric detecting means disposed adjacent the viewing means and adapted to detect whether an object is in front of the viewing means, means controlled by the detecting means for, in effect, short-circuiting the comparator when an object is absent from the viewing means whereby to prevent the sorting being affected by changes in the direct current level of the signal, and means controlled by the comparator for separating from each other the objects which respectively have and fail to have a predetermined colour.

8. A sorting machine for sorting articles by colour comprising means for illuminating an object to be sorted with plane polarised light, a plurality of photoelectric viewing means positioned to receive and view, from a corresponding number of different directions, light reflected from the object so illuminated, means, controlled by the photoelectric viewing means for separating from each other objects which respectively have and fail to have a predetermined colour, an analyser disposed in the path of the light reflected from the object to the photoelectric means, the plane of polarisation of the analyser being crossed with respect to the plane of polarisation of the polarised light produced by the illuminating means, and a plurality of illuminated background elements, supported by a plurality of background element support members which are interconnected so that they may all be simultaneously adjusted in position, whereby the intensity of reflection from the background elements may 'be brought to any desired value, and whereby the distance between the background elements and the illuminating means is variable, the interconnection between said background element support members comprising at least one pair of rotatably mounted members, and two ties interconnecting said rotatably mounted members, one of said ties carrying a background element support member, the ties being so arranged that movement of one rotatably mounted member through a certain angle moves the other rotatably mounted member through the same angle, the two ties being so arranged with respect to each other that there is no dead centre position of the rotatably mounted members.

9. A sorting machine for sorting articles by colour comprising means for illuminating an object to be sorted with plane polarised light, a plurality of photocells positioned to receive and view light reflected from the object so illuminated, means, controlled by the photocells for separating from each other objects which respectively have and fail to have a predetermined colour, an analyser disposed in the path of the light reflected from the object to the photoelectric means, the plane of polarisation of the analyser being crossed with respect to the plane of polarisation of the polarised light produced by the illuminating means, and means for transmitting light from an object being viewed to said photocells, said transmitting means comprising a light conducting member comprising a forked transparent rod having a plurality of limbs which meet substantially at a common point, a photocell being disposed at the outer end of each of the said limbs, said machine comprising a scanning member having a viewing slot, and an objective which focuses an image of an object to be sorted onto one side of said scanning member and lens means on the opposite side of the scanning member for focusing the objective onto 12 the point of separation of the limbs of said forked transparent rod.

10. A sorting machine for sorting articles by colour comprising means for illuminating an object to be sorted with plane polarised light, photoelectric viewing means positioned to receive and view light reflected from the object so illuminated, an analyser disposed in the path of the light reflected from the object to the photoelectric means, the plane of polarisation of the analyzer being crossed with respect to the plane of polarisation of the polarised light produced by the illuminating means, and separating means, controlled by the photoelectric viewing means, for separating from each other objects which respectively have and fail to have a predetermined colour, said separating means comprising ejector means having moving parts for removing the objects which fail to have the said predetermined colour, and means for damping the movement of the moving parts of the ejector means when the said moving parts are returned to their inoperative positions.

11. A sorting machine as claimed in claim 10 in which the ejector means comprises a valve including a valve obturating member for producing a putt of air to remove and article which fails to have a predetermined colour, the damping means serving to damp movement of the valve obturating member.

12. A sorting machine as claimed in claim 10 in which the damping means comprises a container having glass wool or the like disposed therein.

13. A sorting machine for sorting articles by colour comprising means for illuminating an object to be sorted with plane polarised light, photoelectric viewing means positioned to receive and view light reflected from the object so illuminated, and analyser disposed in the path of the light reflected from the object to the photoelectric means, the plane of polarisation of the analyser being crossed with respect to the plane of polarisation of the polarised light produced by the illuminating means, and means, controlled by the photoelectric viewing means, for separating from each other objects which respectively have and fail to have a predetermined colour, said separating means comprising an electronic comparator adapted to distinguish objects which have from those which fail to have a predetermined colour, said comparator being connected to the said photoelectric viewing means so as to be adapted to receive signals therefrom, photoelectric detecting means disposed adjacent the viewmg means and adapted to detect whether an object is in front of the viewing means, and means controlled by the detecting means for in eflect, sho'rt-circuiting the comparator when an object is absent from the viewing means whereby to prevent the sorting being affected by changes in the direct current level of the signal, the separating means also comprising a separating device controlled by the comparator.

14. A sorting machine as claimed in claim 13 comprising a background element whose reflectivity varies from that of the objects in a region of the spectrum outside that to which the photoelectric viewing means are sensitive, the photoelectric detectin means being sensitive to said region.

15. A sorting machine for sorting articles by colour comprising means for illuminating an object to be sorted with plane polarised light, photoelectric viewing means positioned to receive and view light reflected from the object so illuminated, means, controlled by the photoelectric viewing means, for separating from each other objects which respectively have and fail to have a predetermined colour, and analyser disposed in the path of the light reflected from the object to the photoelectric means, the plane of polarisation of the analyser being crossed with respect to the plane of polarisation of the polarised light produced by the illuminating means, at least one background element support member, at least one background element carried by the support member and illuminated by the said illuminating means, and a mask mounted for movement into and out of an interposed position between each background element and said illuminating means.

References Cited in the file of this patent 1 1 Bryce Apr. 2, 1940 Dresser Oct. 9, 1943 Cox Oct. 27, 1953 Martin Dec. 6, 1955 Borsook et a1 Jan. 13, 1959 Cox Mar. 24, 1959 

